Latex paints (pigmented aqueous dispersions of synthetic or natural resins) must contain additives which suppress the formation of foam during their manufacture and use. A principal effect of the additives is to cause rapid deaeration of the paint while the films are wet. It is only in this way that flawless coatings can be obtained which are completely free from foam and bubbles and which completely seal the painted surface. A similar situation exists in the case of oil paints.
The use of defoamers is of decisive importance in the production and use of high gloss latex paints, i.e., paints which provide films of lacquer-like appearance when dry. Latex paints of this type are produced by using resin latices (particularly polyacrylate latices) of very small particle size. Owing to their high content of emulsifying agent, these fine particle size latices readily form foam (particularly the so-called "micro-foam"). Micro-foams are composed of small air bubbles which are enclosed in the surface of the film and thus substantially decrease the glossiness of the film.
Polyadducts of ethylene and propylene oxide, fatty acid polyglycol esters, fatty acid partial esters of glycerine and other polyols such as pentaerythritol, and organopolysiloxanes are widely used as agents for preventing the formation of foam or for breaking foams which have formed. A disadvantage of these anti-foaming agents is their tendency to produce flawed coatings when the paints which have a content thereof are applied to surfaces. The agents impair the adhesiveness and the spreadability of the paint, particularly when the agents are organic silicon compounds. Furthermore, so-called "fish eyes" frequently form in the coatings. Furthermore, the antifoaming effect imparted by the agents is not always adequate.
Defoamers (fine dispersions of certain wax-like substances in an inert carrier liquid, for example, mineral oil) are frequently used to good effect in oil and latex paints. Hydroxystearyl behenate, hydroxystearyl stearate, and the esters of fatty acids with various polyalkylene glycols have given satisfactory results as defoaming agents and usually provide good to adequate results in most paints. However, these defoamers do not perform entirely satisfactorily in high-gloss paints, since they do not prevent formation of the microfoam and do not cause the microfoam to break before the paint has set.